Method of concentrating minerals



Jan. 30, 1945. J HOLT METHOD OF CONCENTRATING MINERALS Filed April 5, 1942 s SheeflsSheet 1 Jan. 30, 1945. J HQLT METHOD OF CONCENTRATING MINERALS Filed April 3, 1942 3 Sheets-Sheet 2 Jan. 30, 1945. G. J. HOLT 2,368,416

METHOD OF CONCENTRATING MINERALS Filed April 5, 1942 3 Sheets-Sheet 3 Patented Jan. 30, 1945 METHOD OF CONCENTRATING MINERALS Grover J. Holt, St. Paul, Mlnn., assignor to Minerals Beneflciation, Incorporated, Joplin, Mo., a

corporation of Delaware Application April 3,1942, Serial No. 437,464 8 Claims. (01. 209-113) This invention relates to the concentration of minerals and particularly those of the finer sizes, my process being an improvement on the invention of Louis J. Erck described in his application Serial No. 395,809, filed May 29, 1941, for Method of concentrating minerals.

It is an object of my invention to provide a novel process of this class whereby three distinct products may be separated and withdrawn from a single tank or trough.

Another object is to provide in a single trough or tank a combination of classifying currents with a thick mass of mineral which is too dense to permit classification depending on particle size and such mechanical agitation of the mass combined with weak upward percolation of water 7 as to produce three products, one comprising fine low density material, another coarse low density material associated with fine high density material, and the third both coarse and fine high density material.

A further object is to regulate the structure and density of the separatory mass in a process of the character described by treating the middlings product containing coarse low density material associated with fine high density material to produce a finer product and returning the latter to the concentrator tank for further hydraulic concentration.

My invention is a continuous process, primarily for concentrating the finer minerals such as those of minus %-inch sizes which contain constituents of a wide range of densities and sizes. I utilize unusually inexpensive machinery and equipment, including a single concentrator from which a middlings product comprising much of the coarser low density material is withdrawn. This product may be treated to produce a finer product and the latter may be returned to the concentrator in which a thick, high density mass is maintained and from which the coarser and lighter material is withdrawn through one out-- let while the finer low density and both coarse and fine high density materials are discharged from other outlets.

My invention will be best understood by refer- .ence to the accompanying drawings in which:

Figure 1 is a diagrammatic illustration of a suitable flow sheet and apparatus for carrying out my invention, the concentrator trough or tank being shown in longitudinal section;

Figs. 2, 3 and 4 are sections taken respectively on the lines 2-2, 33 and 44 of Fig. 1 and showing a typical disposition of the material in the machine;

Fig. 5 is a section through the trough and hutch tanks taken on the line 5-5 of Fig. 4 and showing, diagrammatically, the feed box and lower end outlets; p

Fig. 6 is a diagrammatic illustration of an alternate procedure for treating the separated middlings and returning the treated product to the concentrating machine, and

Fig. 7 is a section taken on the line 11 of Fig. 1 and indicating a typical disposition of the material near the lower end outlets.

Referring to the drawings, my improved concentrating machine has a tank or trough provided with an inclined bottom 1 and a series of hutch tanks 8' extending along the bottom and communicating with the interior of the trough through perforations 9 (Figs. 2, 3 and 5). These tanks are preferably divided longitudinally by partitions l0 and are severally supplied with water under pressure through pipes H, each having a control valve I2, the several pipes ll being connected to a main pipe I3. The sides I4 01 the tank are built up so that a deep pool of water l5 may be maintained to a level substantially above a thick mass of material [6 which is also maintained within the lower end portion of the machine. Stirring and conveying mechanism comprising a screw conveyor having spiral flights I1 is mounted within the trough. The flights II are mounted on an axial shaft [8 and carry on their outer peripheries a series of lifting bars l9 which extend parallel to the shaft l8 substantially from its lower end to approximately the point where it emerges from the pool of water [5.

Communicating with the upper end of the trough is an outlet chute 20 from which the higher density material, both fine and coarse, is discharged as hereinafter described. At the lower end of the trough a weir 2| is provided to receive the overflow water with entrained particles of fine low density material and an outlet conduit 22 communicates with the lower end of the trough at an elevation substantially below the weir 2| to receive the coarser low density material.

As indicated in Fig. 1, the mineral or ore to be concentrated may be fed by a conveyor 23 to a scalping screen 24 which removes particles of sizes larger than those to be treated. As my process may be applied to best advantage to minerals or ores of sizes smaller than %-inch mesh, the screen 24 has openings which exclude the larger sizes while the undersize material from the screen is collected and fed through a conduit 25 and feed box 26 to the concentrator trough,

the point of feed being spaced some distance along the trough from the weir 2|.

From the outlet conduit 22 the middlings product may be fed to an air lift 2'! or pump and delivered by a pipe 28 to a vibrating ocneen 29 of such mesh as to allow the passage through fine screen openings of the fine high density material and any fine low density material that may have been entrained with the coarser high density material. For iron ore concentration the screen 23 should be provided with openings no larger than twenty-eight to the inch and no smaller than forty-eight to the inch. The coarser silica may be discharged from the lower edge of the screen and wasted. It will be understood that the mesh of the screen 29 should be varied to give best results for the particular ore or mineral to be concentrated, with a view to separating a maximum of the coarser middlings product in each case. The maximum particle size of the screen undersize should be approximately equal to the maximum particle size which is discharged through the elevated outlet or over the weir 2!. The fine screen undersize material is collected and fed through a feed box 30 or otherwise into the concentrating machine near the feed box 26. The material so returned for further concentration is largely fine, high density mineral which settles in the pool of water i5, augmenting the dense mass of mineral near the lower end of the trough.

As an alternative procedure for the screening of the middlings they may be ground and returned to the main concentrating machine. As indicated in Fig. 6, a pump 31! receives the middlings from the conduit 22 and discharges them through a pipe 32 which feeds a grinding mill 33. The ground product from the mill 33 may be returned through the feed box 26 to the concentrating machine from which the lower density fraction of the ground material is discharged over the weir 2!. The fine particles of higher density are gradually worked up the incline of the trough and discharged through the outlet chute 20.

To facilitate starting the screw conveyor after a shut down with a mass of mineral in the trough, mechanism is provided for raising the lower end of the shaft l8, carrying the spiral flights, above the bed of mineral in the trough. As illustrated in Figs. 1 and 7, screw operating mechanism of the conventional Akins type: may be employed. The upper end of the shaft!!! has a hearing which is supported on a horizontal pivot pin 34 and the shaft is arranged to be driven through a gear 35 mounted thereon near the pivot bearing. A motor and connections for turning the gear 35 at the desired speed may also be mounted for pivotal movement about the axis of the pin 34 in the usual manner. At its lower end the shaft I 8 is supported in a bearing 36 which is suspended from the lower end of a substantially vertical screw shaft 31 adapted to be raised and lowered by suitable gearing and a crank 38, the shaft being threaded in a nut which is supported on a bracket 39. Guides 36a are provided on the lower end wall of the trough to receive the bearing 36 and guide it in a vertical plane relative to the machine trough. By turning the crank 38 the screw shaft 31 may be moved'longitudinally to raise or lower the shaft I8 carrying .the flights ll, relative to the material in the trough.

In operation the shaft 18 is rotated continuously so that the flights l1 and bars iii are turned slowly in the material in the trough.

(ill

Hutch water from the tanks 8 is fed under pressure through the openings 9 communicating with the bottom of the trough and the supply of hutch water is regulated by the individual valves l2 so that the force of percolating water is insufiicient to produce teetering of the dense mass it in the trough. Mineral oi the sizes to be concentrated passes through the scalping screen 24 and is fed through the conduit 25, together with suflicient water to render it fluid, into the feed box 26 from which it falls into the pool of water i5. As indicated in Figs. 1, 2 and '7, a mass of the mineral I6 is allowed to accumulate near the lower end of the trough and above this mass the pool of water 15 extends to the elevation of the weir 2i. Water is forced up through the solid matter and flows along the trough toward the weir upon the suriace of the mass I6 while the mass is continuously agitated by the flights l1 and bars I 9.

The combined effect of such weak hydraulic currenw, dense mass and mechanical agitation is to concentrate the coarser particles 40 of relatively low specific gravity on or near the surface of the mass IS in a stratum from which it is withdrawn by the conduit 22. The mass i6 constitutes a semi-fluid medium of sufiiciently high density to have a tendency to float the coarser particles 40 but due to the thickness of the mass it isnecessary to agitate it and supply hutch water in order to move such coarse particles to the surface. As hereinbefore pointed out, this mass is too dense to permit classification depending on particle size and the percolating water has insufiicient force to produce teetering of the mass. The finer particles of low density, indicated by the numeral II, are washed out of the heavier mineral by the action of the hutch water which flows toward the rear of the machine and carries the fine material over the weir 2|. In the concentration of iron ore and numerous other ores, the fineparticles 4| are largely sand and may be wasted. The bulk of the concentrated ore 42, comprising both coarse and fine heavy density material, is conveyed to the upper end of the inclined trough bottom I and is discharged through the chute 20 which constitutes an underflow outlet.

As indicated in Figs. 2, 3 and 4, rotation of the flights l'l causes the solid material to be raised somewhat higher on one side of the trough than at the other and from the uppermost hutch box 8 a stream of water flows down the lower side of the material carrying the liberated low density material. Between the outer periphery of the flights l1 and bottom of the trough, a layer 43 of extremely fine high density material accumulates and is retained in the trough as a bed upon which the other material is carried. The coarse low density particles 40, after being discharged from the trough through the conduit 22, may be either screened to separate them from the finer constituents of the middling product, as indl cated in Fig. 1, or, as indicated in Fig. 6, the course particles may be ground and returned to the concentrating machine. With either middlings treatment -a product of such treatment may be returned to the concentrator machine from which the heavier constituents are ultimately discharged into the chute 2c and the lighter particles discharged over the weir 2i.

Where my invention is used for the cleaning of coal it will be understood that the fine coal is discharged over the weir 2| while the coarser particles of coal are recovered from the outlet conduit 22 and slate, pyrite and other relatively high density material is discharged from the chute 20.

Having described my invention, what I claim as new and desire to protect by Letters Patent is:

1. The continuous method of concentrating minerals containing substantial quantities of particles of substantially all size ranges up to the maximum size of the material being treated which comprises subjecting the same to hydraulic concentration in a tank having overflow and underflow outlets and a third outlet communicating with said tank substantially below the level of the overflow outlet and above the bottom of the tank, controlling the rate of feed of material to the tank and the rate of discharge therefrom to maintain a dense mass of solids and water within the tank substantially to the elevation of said third outlet, said mass being too dense to permit classification depending on particle size, subjecting said mass to mechanical agitation causing localized lifting and releasing effects and upward percolation of water having force insulficient to produce teetering of the mass to work the coarser particles of low specific gravity into the upper portion of said mass, discharging said coarser particles of low specific gravity together with some of the finer heavy material and water through said third outlet, maintaining a body of water upon said mass of depth suflicient to permit efiective classification, the surface of said body being substantially at the elevation of said overflow outlet, discharging fine, light particles of mineral into said body of water and out through said overflow outlet and discharging coarse and fine mineral of high specific gravity from the tank through said underflow outlet.

2. The method of concentrating mineral containing substantial quantities of particles of substantially all size ranges up to the maximum size of mineral being treated which comprises subjecting the same to hydraulic concentration in an elongated tank having an overflow outlet communicating therewith near one end, an underflow outlet communicating with the tank near the opposite end and a third outlet communicating therewith substantially below the level of said overflow outlet and above the bottom of the tank, controlling the rate of feed of material to the tank and the rate of discharge therefrom to maintain a dense mass of solids and water within the tank substantially to the elevation of said third outlet, said mass being too dense to permit classification depending on particle size, subjecting said mass to mechanical agitation causing localized lifting and releasing efiects and upward percolation of water having force insuf--v ficient to produce teetering of the mass to work the coarser particles of low specific gravity into the upper portion of said mass, discharging said coarser particles of low specific gravity together with some of the finer heavy material and water through said third outlet, maintaining a body of water upon said mass of depth sufficient to permit effective classification, the surface of said body being substantially at the elevation of said overflow outlet, discharging fine, light particles of mineral into said body of water and out through said overflow outlet and discharging the heavier fraction of mineral from the tank through said underflow outlet.

3. The method of concentrating mineral constantially all size ranges up to the maximum size of mineral being treated which comprises subjecting the same to hydraulic concentration in an elongated tank having an overflow outlet communicating with the tank near one end, a bottom at least a portion of which is inclined, the incline extending to a level above said overflow outlet, an underflow outlet communicating with the tank near the upper end of said inclined bottom and a third outlet communicating therewith substantially below the level of said overflow outlet and above the bottom of the tank near the lower end thereof, controlling the rate of feed of material to the tank and the rate of discharge therefrom to maintain a dense mass of mineral and water within the tank substantially to the elevation of said third outlet, said mass being too dense to permit classification depending on particle size, subjecting said mass to mechanical agitation causing localized lifting and releasing effects and upward percolation of water having force insufficient to produce teetering of the mass to work the coarser particles of low specific gravity into the upper portion of said mass, discharging said coarser particles of low specific gravity together with some of the finer heavy material and water through said third outlet, maintaining a body of water upon said mass of sufiicient depth to permit effective classification, the surface of said body being substantially at the elevation of said overflow outlet, discharging the finer and lighter particles of mineral into said body of water and out through said overflow outlet and conveying the heavier fraction of mineral up said incline and through said underflow outlet.

4.'The continuous method of concentrating minerals containing substantial quantities of particles of substantially all size ranges up to the maximum size of mineral being treated which comprises subjecting the same to hydraulic concentration in a longitudinally inclined, elongated tank having an overflow outlet near its lower end, an underflow outlet near its upper end, a third outlet communicating therewith substantially below the level of said overflow outlet and above the bottom of the tank and a screw conveyor extending longitudinally of the tank to convey mineral to said underflow outlet, said conveyor-having mechanical lifting members, controlling the rate of feed of material to the tank and the rate of discharge therefrom to maintain a dense mass of mineral and water within the tank substantially to the elevation of said third outlet, said mass being too dense to permit classification depending on particle size, subjecting said mass to the mechanical agitation and lifting action of said conveyor and lifting members and to upward percolation of water having force insufiicient to produce teetering of the mass to thereby work the coarser particles of low specific gravity into the upper portion of said mass, discharging said coarser particles of low specific gravity together with some of the finer heavy material and water through said third outlet, maintaining a body of water upon said mass substantially to the elevation of said overflow outlet, discharging the finer and lighter particles of mineral into said'body of water and through said overflow outlet and discharging the heavier fraction of mineral from the tank through said underflow outlet.

5. The method of concentrating mineral actalning substantial quantities of particles of sub- 7 cording claim 1 w n the max m m screening the material from said third outlet to lo separate the coarser constituents thereof and returning the screen undersize material to the mass in said tank.

8. The method of concentrating mineral ac- I cording to claim 1 which includes the steps of grinding the material from said third outlet and returning the ground product to the mass in said.

tank.

GROVER J. HOLT. 

